A type of rotary drill bit used for drilling earth boreholes for the exploration and production of oil and gas and the like is commonly known as a rotary cone drill bit. This type of bit employs a multiplicity of rolling cone cutters, also known as rotary cone cutters, rotatably mounted on bearing pins extending from the arms of the bit. The cutters are mounted on pins that extend downwardly and inwardly with respect to the bit axis so that the conical sides of the cutters tend to roll on the bottom of the borehole and contact the formation. The rows of milled teeth on each cutter are often located in offset relation to the corresponding rows on the other cutters and drill separate tracks at the bottom of the borehole. The milled teeth tend to wear in those areas that engage the bottom and peripheral wall of the borehole during the drilling operation.
The service life of the tooth cutting structure may be improved by the addition of tungsten carbide particles to certain wear areas of the milled teeth. This operation is known as "hardfacing." U.S. Pat. No. 4,262,761, issued Apr. 21, 1981, discloses the application of hardfacing material to a milled tooth, and is hereby incorporated by reference in its entirety. The hardfacing may be designed to create a wear or erosion pattern to produce a self-sharpening tooth profile.
The severe use that drill bits encounter results in the components of the drill bit being repeatedly subjected to much higher stresses, with respect to the ultimate strength of the material, than are commonly encountered in other types of machines. Further, the bits must function profitably in different earth formations, and the geometry of the bit must provide a well balanced cutting structure. The efficient use of available space is also extremely important. The relationship between the cutters is such that a change in the shape or size of any one cutter affects the other cutters. The determination of cone shape or cone contour is also critical.